Glory in tumbled cloudtops on a flight heading south from
Stockholm towards Vienna February 15, 2009. Imaged by
astronomer Franz Kerschbaum (site). ©Franz Kerschbaum, shown with permission.
Droplets near to the uneven cloud surface backscatter and diffract sunlight to form the multi-ringed glory.
Droplets over the entire surface are scattering light backwards but only light from those close to a line from the sun, through the airplane to the clouds reaches the eye or camera to form one's personal glory.
Despite the very uneven clouds and their different distances, the glory rings remain more or less circular and concentric. This tells us that the droplets in the field of view are of similar size. Glories can be non circular when the droplets making them vary in size across the field of view.
Provided that the droplets are the same size it does not matter how far away or near are the clouds. The glory will always have the same angular size and appear the same.
Droplets in the top cloud (diagram at right) contributing light to a red glory ring are located on a small ellipse. An ellipse because the cloud surface is not perpendicular to the direction of the sun's rays. Droplets forming the ring but farther away in the lower cloud are on a larger ellipse. But to the eye both ellipses subtend exactly the same angle, they appear to be the same size - AND the glory looks circular!
Halos and rainbows behave the same way. They keep the same angular size regardless of the distances of their crystals or raindrops. They do not have physical dimensions or distances.